Mukuro, in Ken's body, attempts to attack the collapsed Tsuna and make a contract with him using his trident. But before he is able to stab Tsuna, Tsuna grabs it with his new X-Gloves and claims if he doesn't defeat Mukuro, he can never die in peace. Mukuro jumps back and claims that the special bullet did hit Tsuna, but the flame is much fiercer then the one Tsuna had during the fight with Lancia. Reborn says this bullet is different from Dying Will Bullet, it is the Rebuke Bullet.

The Dying Will Bullet(Left) & The Rebuke Bullet(Right)

With the new Rebuke Bullet, Tsuna attains the Hyper Dying Will Mode, which shifts his erratic despair into a calm, collected state, which is different from Tsuna's wild exposure in Dying Will Mode. Reborn claims that in Hyper Dying Will Mode, his internal senses are enhanced and Tsuna's Hyper Intuition is released, while Dying Will Mode only enhances his body. Mukuro claims it makes no difference and attacks with Ken and Chikusa, which Tsuna takes down easily in his new form, but then Mukuro mocks Tsuna: "You can defeat them, but can you defeat your own friends?". Just then Gokudera and Bianchi attack Tsuna with a barrage of kicks and punches, which Tsuna voluntarily takes. Mukuro starts laughing, saying Tsuna's body will become his. But Reborn says Tsuna is taking the hits to reduce the stress on his friend's body and instinctively he knocked them out and then whispers in their ears apologizing for keeping them waiting.

Mukuro claims the fight isn't finished yet as he gets up in his own body. Mukuro claims that there is one of his six combat skills he hasn't used yet, the fifth path, the path of humans. In Mukuro's opinion, it is the most hideous and disgusting (since he hated the human world the most) and he rather not use it. As he activates it, a dark purple aura surrounds him, giving him a dangerous appearance. Mukuro claims for warriors that fight with auras, the size of their aura is their strength and he attacks Tsuna with his trident stick. Tsuna struggles to hold him back and Mukuro uppercuts him in the stomach, sending him in the air, only for Tsuna to be thrown back, hitting the wall, by his trident stick. Mukuro starts laughing and comments on how weak he is and he is just warming up. Tsuna remarks that he has to be and Mukuro gasps at his new enhanced aura. And Tsuna now gets up with his X-Gloves on fire claiming if that was Mukuro's true power he would've been disappointed. Reborn smiles, realizing that Tsuna finally understands the true purpose of his X-Gloves, since they are made from the same material as the Dying Will Bullet (because they were all born from Leon) so they can light the Dying Will Flame as well. Mukuro then compares Tsuna to a cat who puffs up his fur to seem bigger and that changing his aura is useless.

Tsuna remarks that the Dying Will Flame isn't an aura but Mukuro doesn't believe him and asks him to show him as Mukuro charges at him. Tsuna grabs his stick with his glove and he heats it up, easily bending it and even making Mukuro feel the heat which surprises him that his aura is emitting heat. Reborn responds that the energy density between an aura and the Dying Will Flame is too great and unlike an aura (which can be seen by only special people) the Dying Will Flame has its own destructive property, it's super condensed energy. Mukuro realizes that his gloves can burn but Tsuna replies that there is more and charges at him. But Mukuro tries to intercept him with his stick but Tsuna disappears behind him, Mukuro starts screaming that it is impossible to disappear as Reborn smiles. Tsuna punches him sending him flying and as he gets up he is still wondering how Tsuna disappeared. Tsuna, confident, asks him if he is done warming up, making Mukuro laugh, claims that with Tsuna's body, without scheming, he can just attack mafia families directly and cause a war in the mafia. Reborn concludes that, that is Mukuro's true goal but he remarks that he is not so small minded and that his true goal is to posses every important person in the world and through them he will paint the world in a pure and beautiful darkness, a world war. But first he wants to eradicate the mafia only for him to be questioned by Reborn and Tsuna as to why he is so obsessed with the mafia and if he holds a grudge against them.

Mukuro replies he will give no more further information and that Tsuna will become his. Mukuro sends an illusion flying at him which Tsuna realizes but he gets hurt by the rocks in the illusion as Reborn calls him stupid and to pay attention. Tsuna rubbing his eye in pain as Mukuro jumps in the air thinking he got him. However, Tsuna lights up his gloves, again disappears behind Mukuro and punches him to the ground. Greatly injured, Mukuro stares at him, claiming that Vongola the tenth is the man who defeated him and tells Tsuna to finish him off, but Tsuna refuses, turning around and walking away from him. Mukuro starts to smile and grabs Tsuna in a lock claiming that his softness will get him killed. Mukuro attacks him as Tsuna is unable to use his arms and Mukuro claims the reason he sent so many assassins after Tsuna was because he got draw out his power and then take over him. Mukuro now throws Tsuna into the trident stick which is stuck in wall and claims that Tsuna cannot maneuver in midair and he will lose because of his kindness. Reborn yells at Tsuna and tells him to show Mukuro the true power of the X-Gloves and Tsuna screams, lighting the gloves, and thrusts himself forward and away from the trident (High speed maneuvering and using the flame as propulsion) and to Mukuro. Mukuro realizes that is how he disappeared before and Tsuna grabs him and slams him to the wall, knocking him unconscious and ending the battle.

Tsuna defeats Mukuro

Reborn smiles, claiming the Dying Will Flame cleansed the ugly, black aura. Tsuna gets up realizing it's over and enters out of Hyper Dying Will Mode. Tsuna finally remembers that his friends are hurt and starts panicking, but Reborn reassures him, claiming the Vongola medical team has arrived and that they were able to find an antidote to Lanchia's poison. Outside, everyone is being treated by the Vongola doctors and taken to an ambulance. Back inside, Tsuna is relieved but asks Reborn if Mukuro is alive and if he is okay, which Reborn calls him as soft as ever. Then suddenly, Ken and Chikusa regain consciousness, but due to their injuries, they crawl to and scream at Tsuna to stay away from Mukuro. Tsuna is puzzled and ask them why they are going so far for Mukuro since their bodies were possessed by him. They reply that their pain is nothing to what they endured back then, attempting to stand up. Tsuna and Reborn ask they what happened to them that made them hate the mafia so much, which Ken replies they were used for experiments by their own family. Reborn concludes that they are from the Estraneo Famiglia (the same family that created the Possession Bullet that was made forbidden in the mafia world).

Ken starts to explain that it was made forbidden for the other families convenience and because of that his family was being destroyed, Ken starts to have a flashback, so in order to survive they tried to invent special weapons so they began to experiment on the kids of their family (including Ken, Chikusa, and Mukuro). They experienced day and day of cruel experiments, with no end and no escape, but one day Mukuro finally broke free and killed the family and he asked Ken and Chikusa if they would like to come along with him (that was the first time Ken and Chikusa heard his voice since he was always quiet) and they agreed because that was their place to be and they won't let Tsuna destroy it. After hearing this, Tsuna feels depressed but replies that he won't let them hurt his friends because that's his place to be. Suddenly, the Vindice, the protectors of mafia law appear, which Tsuna mistakes for the medical team, but Reborn replies that its not them. Instead they capture Ken, Chikusa, and the unconscious Mukuro which shocks Tsuna and tells them to stop but Reborn replies its no use, since defying them will be trouble. Tsuna starts wondering what is going to happen to them and Lanchia, which Reborn replies they will be judged and punished and it won't be light either. That is when the medical team arrives to treat the injured. Just then Tsuna starts feeling a jolt of pain all over his body and drops to the floor and makes him wonder what is going on and Reborn answers that combat using the Rebuke bullet is very hard on the body and the stress has come back as pain. Tsuna starts screaming in pain and faints from too much pain, which makes Reborn say that he still needs to train him more but he overcame the Vongola 9th's trial and well done. Reborn then falls asleep next to him.

1 month later, Hibari is sleeping on the roof of the school and Hibird starts calling him, but Hibari sends it away. Hibird then flies away singing the school song. The rest of the gang is watching Yamamoto's baseball game and cheering him on, except Gokudera, who starts yelling at him, calling him a baseball nut and is then joined by Ryohei, but Ryohei instead is trying to get the baseball players to join the boxing club. Suddenly, a ball is being hit towards Tsuna but Bianchi comes just in time and catches it, making Gokudera faint. It turns out that she only came to bring lunch for everyone and Haru replies that she also made lunch only for Tsuna, but Lambo takes it and starts running around while being chased by I-Pin. Tsuna sighs, wondering why this always happens, to which Fuuta responds by laughing and saying he is happy they are all spending time together. Tsuna agrees but

Mukuro returns!

starts to feel strange, and turns but sees nothing out of the ordinary and wonders if it was just his imagination. He then starts attending to Lambo, who is crying because the lunch was destroyed. Meanwhile, Reborn stares at a small boy and his mother who are leaving the stadium and talking about the boy's big brother, one of the baseball players, and their dinner that night. Reborn smiles, claiming it is lonely being by yourself and that he will take him on anytime. The boy whispers "One day" and turns around to reveal that he is being possessed by Mukuro, thus bringing an end to the Kokuyo Arc.